Many systems for oxygen injection from furnace walls are known. A number of such systems make use of an additional flame to regulate the initial heating and melting of the metal charge, which is usually activated by natural gas as the fuel and oxygen as the supporter of combustion.
The drawback of the models currently available is that the devices described do not allow varying the shape of the flame at will in the various melting procedure phases.
At the start of the melting process, a diffuse and wide flame is notably needed in order to uniformly distribute a large chemical power throughout the solid charge. Subsequently, a concentrated flame mode is required, which is adapted to transfer heat to the residual solid charge below the injector installation level.
No state of the art injection device is known which is adapted to regulate the shape of the flame between these two opposite typologies. In particular, electric arc furnaces, hereinafter referred to as EAF, in which the state of the art injectors are used, suffer from bad heat distribution. The type of burners (and injectors in burner mode) typically used in EAF produce a concentrated flame that produces somewhat inefficient blending and oxidises the charge in the initial phases of the melting process.
When used in burner mode, the known injectors present large fractions of free oxygen in the flame, a characteristic that, combined with the strongly localised heating effect of the flame on the charge, makes them machines suitable for oxygen lance cutting the metal charge, but not for heating it uniformly. The oxidation of the charge in the initial phases of the melting process causes serious losses to the global energy balance as well as a drop in the final metallic yield.
Further drawbacks of this type of device are caused by the concentration of the flame produced. The volume of the heated metal charge remains limited, whereas the perforation of the charge as far as the electric arc area is a frequently observed phenomenon, which results in the disturbance of the arc and causes the burnt gases to rise up along the electrode without passing through the charge, to which heat is not transferred efficiently. Moreover, the ring of metal charge at the base of the column present in the furnace is preheated in a discontinuous way, with the consequence that the furnace must contain a greater number of injectors.
In addition to these limits in burner mode, the injectors currently available are also not efficient in the injection of supersonic oxygen, carbon and lime.
The installation of such injectors on the walls of EAF requires that the jets produced by the injector are coherent, at least with regards to the distance between injector and liquid bath. This characteristic is not satisfied by the state of the art devices when the installation distance from the bath is greater than 750 mm. As a consequence, the oxygen, carbon and lime injections into the liquid bath and the slag are inefficient, with a consequential lengthening of refining times and the thermal overload of the internal volume of the furnace and the fume system caused by the reagents dispersed above the bath.
No state of the art injectors are known which are adapted to injecting fuel such as methane into the slag and/or molten bath in order to give a carburation reaction of the bath and simultaneously develop heat and reduce the oxides in the slag.
Patent documents GB-A-2064094 discloses a burner having holes through which fluent fuel can be discharged within an outwardly divergent envelope and further passages encircling the first passage through which an atomising fluid can be discharged into the fuel as it leaves the burner head. U.S. Pat. No. 6,289,677 discloses a fuel injector for a gas turbine engine with a nozzle tip including an annular array of air passages spaced radially from a central fuel injector passage. The axes of the passages are arranged so as to permit mixing of air and fuel. A second annular array of air passages is provided to produce a circular shape of the flame.
The shape of the flame produced by such burners of the known art is circular and not suitable for hitting a surface from above whereby part of the energy is dissipated above the surface. Furthermore it cannot eject gas at supersonic velocity.